Catalytic device for watercraft engine

ABSTRACT

A watercraft is provided with an engine. An exhaust system routes exhaust gases from the engine to an external location. The exhaust system has an exhaust conduit and a catalytic device affixed to the exhaust conduit. The catalytic device has a tubular member that extends in the exhaust conduit. Two intermediate members extend in the tubular member one after another along a flow direction of the exhaust gases. The tubular member supports each intermediate member. The catalytic device has two catalysts. Each intermediate member is affixed to the tubular member at one end thereof and supports each catalyst at another end thereof.

PRIORITY INFORMATION

[0001] This application is based on and claims priority to JapanesePatent Application No. 2001-384355, filed on Dec. 18, 2001, the entirecontents of which is hereby expressly incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates generally to a catalytic device for anengine and, more particularly, to an improved catalytic device for anengine that incorporates a plurality of catalysts.

[0004] 2. Description of Related Art

[0005] Personal watercrafts have become very popular in recent years.This type of watercraft is quite sporting in nature and carries one ormore riders. A hull of the watercraft typically defines a rider's areaabove an engine compartment. An internal combustion engine powers a jetpropulsion unit that propels the watercraft by discharging waterrearward. The engine lies within the engine compartment in front of atunnel which is formed on an underside of the hull. The jet propulsionunit is placed within the tunnel and includes an impeller that is drivenby the engine.

[0006] The watercraft is provided with an exhaust system to routeexhaust gases from the engine to a location outside the watercraft. In atypical arrangement, the exhaust system comprises exhaust conduitsconnected in series and the last conduit opens to the tunnel todischarge the exhaust gases thereto.

[0007] The exhaust system can be provided with a catalytic device thatincorporates a catalyst therein to remove unburned gases such ashydrocarbon (HC), carbon monoxide (CO) and nitrogen oxides (NOx) fromthe exhaust gases. The catalytic device is disclosed in, for example,U.S. Pat. Nos. 5,787,847, 5,797,775 and 5,983,631, and JapaneseLaid-Open Patent Publications Nos. 11-303628 and 2000-130182.

[0008]FIG. 1 illustrates an exemplary catalytic device, which is shownin section along with a sectioned portion of an exhaust conduit 20. Theexhaust conduit 20 extends from an engine (not shown) to define anexhaust passage 22 that routes exhaust gases from the engine. Theexhaust conduit 20 also defines a water jacket 24 around at least asection of the exhaust passage 22. A tubular member 26 extends withinthe exhaust passage 22 and has a circular flange 28 that is affixed tothe exhaust conduit 20 with gaskets 30 disposed on both sides of theflange. An intermediate member 32 coaxially extends within the tubularmember 26. The intermediate member 32 is brazed to the tubular member 26with solder 34 at one end thereof. The intermediate member 32 holds acatalyst 36. The catalyst 36 is brazed to the intermediate member 32with solder 38 at another end of the intermediate member 32. Retainers40 are attached to both ends of the tubular member 26 to prevent thecatalyst 36 from moving from the original position should either thecatalyst 36 break from the intermediate member 32 or the intermediatemember 32 break from the tubular member 26, due to vibration.

[0009] The catalyst 36 has a length L that makes the catalyst 36relatively large and heavy in weight. The solders 34, 36 thus arerequired to be sufficiently long to support the intermediate member 32and the catalyst 36, respectively. In addition, the retainers 40 have awidth W that is necessary to keep the catalyst 36 in the originalposition. However, the larger the width W of the retainers 40, thesmaller the effective area of the catalyst 36.

[0010] A need therefore exists for a catalytic device that can securelyhold a catalyst in place while maximizing an effective area of thecatalyst.

SUMMARY OF THE INVENTION

[0011] In accordance with one aspect of the present invention, awatercraft comprises an internal combustion engine. An exhaust system isarranged to route exhaust gases from the engine to an external location.The exhaust system comprises an exhaust conduit and a catalytic deviceaffixed to the exhaust conduit. The catalytic device comprises a supportmember extending in the exhaust conduit and a plurality of catalystssupported by the support member. The catalysts are disposed one afteranother along a flow direction of the exhaust gases.

[0012] In accordance with another aspect of the present invention, awatercraft comprises an internal combustion engine. An exhaust system isarranged to route exhaust gases from the engine to an external location.The exhaust system comprises an exhaust conduit and a catalytic deviceaffixed to the exhaust conduit. The catalytic device comprises a firstsupport member extending in the exhaust conduit. A plurality of secondsupport members extend at least partially within the first supportmember and are arranged one after another along a flow direction of theexhaust gases. The first support member supports each of the secondsupport members. A plurality of catalysts are provided. Each catalyst issupported by a respective one of the second support members.

[0013] In accordance with a further aspect of the present invention, acatalytic device is provided for an internal combustion engine. Thecatalytic device comprises a tubular member adapted to be disposedwithin an exhaust conduit of the engine. A plurality of catalystsextends in series with one another. The catalysts are spaced apart fromeach other and are disposed, at least in part, within the tubularmember.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1, as noted above, is an enlarged sectional view of anexemplary catalytic device placed within an exhaust conduit. This figureis provided in order to assist the reader's understanding of problems inthe related art.

[0015] FIGS. 2-10 illustrate preferred embodiments of the presentcatalytic device that are intended to illustrate, but not to limit, theaforementioned and other features, aspects and advantages of the presentinvention. The following briefly describes each of these additionalfigures.

[0016]FIG. 2 is a partially sectioned, side elevational view of apersonal watercraft configured in accordance with a preferred embodimentof the present invention.

[0017]FIG. 3 is a cross-sectional view taken along the line 3-3 of FIG.2.

[0018]FIG. 4 is a top plan view of an engine and a section of an exhaustsystem of the personal watercraft of FIG. 2.

[0019]FIG. 5 is an enlarged sectional view of an exhaust conduit of theexhaust system that incorporates a catalytic device. The catalyticdevice is not sectioned in this figure.

[0020]FIG. 6 is an enlarged sectional view of the exhaust conduit andthe catalytic device. A portion of the exhaust conduit that defines awater jacket is shown in this figure.

[0021]FIG. 7 is another enlarged sectional view of the exhaust conduitand a catalytic device that is configured in accordance with anotherpreferred embodiment of the present invention. Another portion of theexhaust conduit, which defines a fixing construction of the catalyticdevice to the exhaust conduit, also is shown in this figure.

[0022]FIG. 8 is a schematic sectional view of a catalytic device that isconfigured in accordance with an additional preferred embodiment of thepresent invention.

[0023]FIG. 9 is a schematic sectional view of a catalytic device that isconfigured in accordance with a further preferred embodiment of thepresent invention.

[0024]FIG. 10 is an enlarged sectional view of another modifiedcatalytic device that is configured in accordance with a preferredembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

[0025] With reference to FIGS. 2-5, an overall construction of apersonal watercraft 50 that incorporates a catalytic device 52configured in accordance with a preferred embodiment of the presentinvention will be described. The catalytic device has particular utilitywith the personal watercraft, and thus is described in the context ofthe personal watercraft. The catalytic device, however, can be appliedto other types of watercrafts as well, such as, for example, but withoutlimitations, small jet boats and the like. Furthermore, certain aspectsand features of the catalytic device also can be applied to land vehicleand stationary engines.

[0026] The personal watercraft 50 includes a hull 56 generally formedwith a lower hull section 58 and an upper hull section or deck 60. Thelower hull section 58 can include one or more inner liner sections tostrengthen the hull 56 or to provide mounting platforms for variousinternal components of the watercraft 50. Both the lower and upper hullsections 58, 60 are made of, for example, a molded fiberglass reinforcedresin or a sheet molding compound. The lower hull section 58 and theupper hull section 60 are coupled together to form an internal cavitywhich wholly or partially defines an engine compartment 59. Anintersection 62 of the hull sections 58, 60 is defined in part along anouter surface gunwale or bulwark. The hull 56 houses an internalcombustion engine 64 that powers the watercraft 50. The engine 64 isdisposed within the engine compartment 59.

[0027] The lower hull section 58 is designed such that the watercraft 50planes or rides on a minimum surface area at the aft end of the lowerhull 58 in order to optimize the speed and handling of the watercraft 50when up on plane. For this purpose, the lower hull section 58 generallyhas a V-shaped configuration formed by a pair of inclined sections thatextend outwardly from a longitudinal center line of the hull 56 to thehull's side walls at a dead rise angle. Each inclined section desirablyincludes at least one strake and the strakes preferably aresymmetrically disposed relative to the keel line of the watercraft 50.The inclined sections also extend longitudinally from the bow toward thetransom of the lower hull 58. The side walls are generally flat andstraight near the stem of the lower hull 58 and smoothly blend towardthe longitudinal centerline at the bow. The lines of intersectionbetween the inclined sections and the corresponding side walls form theouter chines of the lower hull section 58.

[0028] A steering mast 66 extends generally upwardly toward the top ofthe upper hull section 60 to support a handlebar 68. The handlebar 68 isprovided primarily for a rider to control the steering mast 66 so that athrust direction of the watercraft 50 is controlled. The handlebar 68also carries control devices such as, for example, a throttle lever foroperating throttle valves of the engine 64.

[0029] A seat 72 extends fore to aft along a center plane of the hull 56at a location behind the steering mast 66. The center plane extendsgenerally vertically with the watercraft resting in normal uprightposition. The seat 72 has generally a saddle shape so that the rider canstraddle it. The illustrated upper hull section 60 defines a seatpedestal 73 and the seat 72 is detachably placed or hingedly affixed tothe seat pedestal 73. Foot areas 74 are defined on both sides of theseat 72 and at the top surface of the upper hull section 60. An accessopening 76 (FIG. 3) is defined on the top surface of the seat pedestal73 under the seat 72. The rider thus can access the engine compartment59 through the access opening 76.

[0030] The upper hull section 60 defines a storage recess in front ofthe steering mast 66 and a hutch 76 is hinged to open or is detachablyaffixed to the upper hull section 60 to close the storage recess. A fueltank 78 is placed in the internal cavity under the upper hull section 60and preferably in front of the engine 64. The fuel tank 78 is coupledwith a fuel inlet port positioned at a top surface of the upper hullsection 60 through a filler duct 80. A closure cap 82 closes the fuelinlet port.

[0031] Air ducts or ventilation ducts 86 are provided at appropriatelocations of the upper hull section 60 so that the ambient air can enterthe internal cavity through the ducts 86. Except for the air ducts 86,the engine compartment 59 is substantially sealed so as to protect theengine 64 and engine related components from water.

[0032] A jet pump assembly 88 propels the watercraft 50. The jet pumpassembly 88 is mounted in a tunnel or pump housing 90 formed on theunderside of the lower hull section 58. Optionally, the tunnel 90 can befurther isolated from the engine compartment 59 by a bulkhead. Thetunnel 90 has a downward facing inlet port 92 opening toward the body ofwater. A bottom plate 94 closes the lower hull section 58 except for theinlet port 92 of the tunnel 90.

[0033] The jet pump assembly 88 includes an impeller 96 that isjournaled within the tunnel 90. An impeller shaft 98 extends forwardlyfrom the impeller 96 and is coupled with an output shaft 100 thatextends from the engine 64 by a coupling unit 102 to be driven by theoutput shaft 100.

[0034] The rear end of the pump assembly 88 defines a discharge nozzle106. A deflector or steering nozzle 108 is affixed to the dischargenozzle 106 for pivotal movement about a steering axis that extendsgenerally vertically. A cable connects the deflector 108 with thesteering mast 66 so that the rider can move the deflector 108.

[0035] When the output shaft 100 of the engine 64 drives the impellershaft 98 and the impeller 96 thus rotates, water is drawn from thesurrounding body of water through the inlet opening 92. The pressuregenerated in the pump assembly 88 by the impeller 96 produces a jet ofwater that is discharged through the discharge nozzle 106 and thedeflector 108. The water jet thus produces thrust to propel thewatercraft 50.

[0036] The engine 64 in the illustrated embodiment operates on atwo-cycle crankcase compression principle and has three cylinders 112,114, 116 (FIG. 4) spaced apart from one another along the longitudinalcenter plane. The illustrated engine, however, merely exemplifies onetype of engine with which the catalytic device can be used. Other typesof engines having other number of cylinders, having other cylinderarrangements, other cylinder orientations (e.g., upright cylinder banks)and operating on other combustion principles (e.g., four-cycle orrotary) can of course be applied.

[0037] The engine 64 typically comprises a cylinder block defining threecylinder bores that correspond to the three cylinders 112, 114, 116. Apiston reciprocates in each cylinder bore. At least one cylinder headmember is affixed to the upper end of the cylinder block to closerespective upper ends of the cylinder bores and defines three combustionchambers with the cylinder bores and the pistons. A crankcase member isalso affixed to the lower end of the cylinder block to close therespective lower ends of the cylinder bores and to define crankcasechambers with the cylinder block. A crankshaft is rotatably connected tothe pistons through connecting rods and is journaled for rotation withinthe crankcase member. The foregoing output shaft 100 is coupled with thecrankshaft through an appropriate transmission mechanism. The cylinderblock, the cylinder head and the crankcase member preferably are made ofaluminum alloy and together define an engine body.

[0038] Engine mounts 120 extend from both sides of the engine body. Theengine mounts 120 preferably include resilient portions made of, forexample, rubber material. The engine body is mounted on the lower hullsection 58 (or possibly on the hull liner) by the engine mounts 120 sothat vibration of the engine body is inhibited from transferring to thehull section 58.

[0039] The engine 64 preferably is provided with an air induction systemto introduce air into the crankcase chambers from within the enginecompartment 59. With reference to FIGS. 3 and 4, the illustrated airinduction system includes a first intake box 124 and a second intake box126. The first intake box 124 is located in front of the engine 64 andthe second intake box 126 is located on the starboard side relative tothe engine 64. A connecting conduit 128 connects both the first andsecond intake boxes 124, 126 together. The first and second intake boxes124, 126 define first and second plenum chambers therein, respectively.The first intake box 124 also defines an inlet port 129 through whichthe air in the engine compartment 59 is drawn into the first plenumchamber. On the other hand, the second plenum chamber of the secondintake box 126 is coupled with intake ports of the crankcase chambersthrough three carburetors 130.

[0040] Each carburetor 130 incorporates a throttle valve to measure anappropriate amount of air that is delivered to the associated combustionchamber. With the throttle valve measuring the air amount, thecarburetors 130 supply fuel to the crankcase chambers to form anair/fuel charge in each crankcase chamber. An amount of the fuel also ismeasured by the carburetor 130. The fuel amount changes in proportion tothe air amount measured by the throttle valves so that a proper air/fuelratio can be held. Alternatively, the engine 64 can employ other chargeformers such as, for example, a fuel injection system.

[0041] An intake valve such as a reed valve, for example, controls eachintake of the air/fuel charge into the crankcase chamber. Each crankcasechamber is connected to each combustion chamber through a scavengepassage and a scavenge port. The air/fuel charge is pre-compressedwithin the crankcase chamber and then is drawn into to the combustionchamber through the scavenge passage and port.

[0042] An ignition or firing system preferably is provided to ignite theair/fuel charges in the combustion chambers. The ignition systempreferably includes spark plugs that have electrodes exposed into thecombustion chambers and an ignition device that supply ignition power tothe spark plugs. In the illustrated embodiment, high-tension cables 134(FIG. 4) are used to supply the ignition power to the respective sparkplugs. The spark plugs fire the air/fuel charges in the combustionchambers by sparks made by the ignition devices at proper ignitiontimings controlled by an ECU (electronic control unit) or other controlunits.

[0043] The engine 64 also is provided with an exhaust system to routeburnt charges, i.e., exhaust gases, from the combustion chambers to alocation outside of the watercraft 50. An exhaust manifold 138preferably is coupled with exhaust ports of the combustion chambers.More specifically, three branched portions of the manifold 138 areconnected to the respective exhaust ports. A fresh air/fuel charge thatenters each combustion chamber pushes the exhaust gases out the exhaustport and into the exhaust manifold 138.

[0044] In the illustrated embodiment, a first exhaust conduit 142 iscoupled with a common end of the exhaust manifold 138 downstream of thebranch portions. The first exhaust conduit 142 extends generally aroundand above the front end of the engine 64. The exhaust conduit 142 thenturns generally rearward and extends along the cylinder block of theengine 64 on the starboard side and generally above the second intakebox 126. The exhaust conduit 142 again turns toward the port side in therear of the engine 64 and then is generally oriented rearwardly.

[0045] An exhaust silencer or water-lock unit 146 preferably is placedat a location generally behind the engine 64 and is secured to the lowerhull 58 (or possibly to a hull linear). The exhaust silencer 146 also ispositioned on the port side relative to the longitudinal center plane.The distal end of the first exhaust conduit 142 is connected to an inletport of the exhaust silencer 146 defined at a front surface thereof.

[0046] A second exhaust conduit 150 extends generally upwardly from atop surface of the exhaust silencer 146 and further extends toward thestarboard side of the watercraft 50 beyond the longitudinal centerplane. The second exhaust conduit 150 ends at a discharge port thatopens at the tunnel 90 and thus to the exterior of the watercraft 50.The discharge port preferably is positioned at a location that can beout of the body of water in the event the watercraft 50 capsizes.

[0047] The exhaust gases can be discharged through the exhaust manifold138, the first exhaust conduit 142, the exhaust silencer 146 and thesecond exhaust conduit 150. Because of the arrangement of these exhaustcomponents, entry of outside water into the engine 64 is inhibited evenif the watercraft 50 capsizes or floats at other positions on the bodyof water.

[0048] The first and second exhaust conduits 142, 150 can be formed withmultiple conduit sections, respectively. The illustrated first exhaustconduit 142, for example, comprises at least four conduit sections 142a, 142 b, 142 c, 142 d (FIG. 4). A catalytic device 154, which will bedescribed in greater detail below, is placed between the conduitsections 142 c, 142 d. The conduit sections 142 c, 142 d preferably forma large diameter portion 153 to incorporate the catalytic device 154therein. The illustrated large diameter portion 153 is formed next tothe second and third cylinders 114, 116 so that the rider can easilyaccess to the catalytic device 154 through the access opening 76. Therespective conduit sections 142 a, 142 b, 142 c, 142 d preferably aresupported by the engine body. For instance, as shown in FIG. 3, theconduit sections 142 b, 142 c, which defines the large diameter portion153, are affixed by bolts 177 to vertical stays 155 and horizontal stays156 both extending from the engine body.

[0049] With particular reference to FIGS. 4 and 5, the watercraft 50preferably is provided with a typical open-loop type water coolingsystem for the engine 64 and the exhaust system. The cooling water isintroduced into the system from the body of water.

[0050] In the illustrated embodiment, the cooling system preferablyincludes a water intake conduit that communicates with a water jacketdefined in the exhaust manifold 138. The cooling water is delivered atleast to water jackets formed within the engine body to cool engineportions which build heat therein. A water jacket 158 also is definedwithin the first exhaust conduit 142 and preferably is formed around anexhaust passage 160 coaxially. Water pipes 162 connect the water jacketsof the engine body with the water jacket 158 of the first exhaustconduit 142. In the illustrated arrangement, flexible members 164 suchas rubber tubes, for example, couple the conduit sections 142 b, 142 cso as to complete the exhaust passage 160 and the water jacket 158.

[0051] The water jacket 158 ends at an appropriate downstream locationin the conduit section 142 d and opens to the exhaust passage 160. Thewater thus is mixed with the exhaust gases and is delivered to theexhaust silencer 146. The water finally is discharged to the body ofwater through the second exhaust conduit 150 with the exhaust gases.

[0052] With continued reference to FIGS. 2-5 and with additionalreference to FIGS. 6 and 7, the catalytic device 154 will now bedescribed in greater detail below.

[0053] The illustrated catalytic device 154 comprises at least twocatalysts 170, 172, at least one a main tubular member or first supportmember 174, and at least two intermediate tubular members or secondsupport members 176.

[0054] The catalysts 170, 172 can be oxidation catalytic converters,three-way catalytic converters or any other catalytic converters. Eitherthe same type or different types of the catalytic converters can beselected for each catalyst 170, 172. In the illustrated arrangement,each catalyst 170 has a honeycomb configuration and is shapedcylindrically about an axis 177 that extends along a flow direction ofthe exhaust gases. Both the catalysts 170, 172 have a length L1 alongthe axis 177.

[0055] The tubular member 174 is made of metal material and is formedwith a cylindrical section 179 and at least one a flange section 180that extends from the cylindrical section 179, preferably at a midportion thereof. The cylindrical section 179 has a center axis thatpreferably is generally collinear with the axis 177 when the catalysts170, 172 are placed in a preset position. The cylindrical section 179has a length L2 along the center axis 177. The length L2 is greater thana total amount of the lengths L1 of the catalysts 170, 172. The lengthL2 preferably is equal to the length L of the single catalyst 36 ofFIG. 1. The flange section 180 can be formed separately from thecylindrical section 179 and welded thereto. The flange section 180 isinterposed between the conduit sections 142 b, 142 c with gaskets 184disposed on both sides. Slots 186 are formed in the illustrated flangesection 180 such that the water from the water jacket 158 can flowthrough the flange section 180. A pair of notches 188 (FIG. 3) also isformed next to two of the slots 186 to place the tubular member 174 in apreset position. Bolts 190 are inserted into bolt holes defined betweenthe slots 186, and nuts 191 securely fix the bolts 190 in the positions.

[0056] The intermediate members 176, 178 also are made of metal materialand are thinner than the tubular member 174. Each intermediate member176, 178 preferably has a cylindrical shape similar to that of (butsmaller in diameter than) the cylindrical section 179 of the tubularmember 174. The intermediate members 176, 178 are interposed between thetubular member 174 and the respective catalysts 170, 172. That is, theintermediate members 176, 178 have a diameter that is smaller than adiameter of the tubular member 174 and is larger than a diameter of thecatalysts 170, 172. The illustrated intermediate members 176, 178 havegenerally the same length L1 as the catalysts 170, 172.

[0057] Each intermediate member 176, 178 is brazed with the tubularmember 174 by solder 192 at one end 194 thereof and also is brazed witheach catalyst 170, 172 by solder 196 at another end thereof 198. In thisdescription, the one end 194 where the intermediate member 176, 178 isbrazed with the tubular member 174 is called as a “first end” 194 andthe another end 198 which is opposite to the first end 194 is called asa “second end” 198. In a similar manner, an end 200 of each catalyst170, 172 where the catalyst 170, 172 is brazed with the intermediatemember 176, 178 is called as a “first end” 200 and the another end 202which is opposite to the first end 200 is called as a “second end” 202.That is, the first end 200 of the catalyst 170, 172 is affixed to thesecond end 198 of the intermediate member 176, 178. “First” and “second”thus are not used in relation to the direction of exhaust flow and canrefer to different ends on the catalysts and/or the intermediatemembers. For example, in the illustrated embodiment, the first end 200of the upstream catalyst 170 is on the downstream side of the catalyst170, while the first end 194 of the corresponding intermediate member176 is located on the upstream side. In other embodiments, for examplethe embodiment shown in FIG. 8 (which will be described later), thefirst end 200 of the upstream catalyst 170 is located on the downstreamside of the catalyst 170 while the first end 200 of the downstreamcatalyst 172 is located on the upstream side of the catalyst 172.

[0058] Because of the arrangement, in the illustrated embodiment, theupstream catalyst 170 is positioned in front of the downstream catalyst172 in the exhaust flow and the first end 200 of the catalyst 170 isspaced apart from the second end 202 of the catalyst 172 by a distanceD1. Preferably, the distance D1 is between approximately 2-10% of thelength L1 of the catalyst 170, 172.

[0059] Each intermediate member 176, 178 is spaced apart from thetubular member 174 by a distance D2, while each catalyst 170, 172 isspaced apart from the intermediate member 176, 178 by a distance D3. Thedistances D2, D3 can be generally equal to each other and preferably areless than the distance D1.

[0060] Although not shown, each intermediate member 176, 178 preferablyhas slits that extend in a direction of the axis 177 and that are evenlyspaced about the intermediate member relative to the axis 177 (e.g.,about the circumference of the intermediate member). Each slot extendsfrom the second end 198 toward the first end 194, but stops well shortof the first end 194 so as to not to provide an uninterrupted area forthe solder 192. The slots, however, form cantilever sections at thesecond end 198 to which the solder 196 is applied. Thus, theintermediate members 176, 178 can absorb thermal expansion and shrinkageof the catalyst bodies 170, 172 and can elastically suspend thecatalysts 176, 178 such that the catalysts 170, 172 can move radially(i.e., in a direction normal to the axis 177).

[0061] The exhaust gases coming from the upstream portion of the exhaustpassage 160 flows first through the upstream catalyst 170 and then flowsthrough the catalyst 172. Unburned gases such as hydrocarbon (HC),carbon monoxide (CO) and nitrogen oxides (NOx) in the exhaust gases areeffectively neutralized by those catalysts 170, 172.

[0062] The usage of the intermediate members 176, 178 and the cantilevertype support construction of the catalysts 170, 172 and the intermediatemembers 176, 178 inhibit mechanical vibrations within the structure ofthe first exhaust conduit 142 from transferring to the catalysts 170,172, i.e., the support structure dampens such vibrations.

[0063] Because the illustrated catalysts 170, 172 are separatelyprovided, each catalyst 170, 172 can have less weight than a singlecatalyst. Thus, the solders 192, 196 do not need to bear heavycatalyst(s) and the risk that the solders 192, 196 will fail is reduced.No retainers are necessary to hold the catalysts 170, 172. The catalysts170, 172 thus can be held in the original position and the effectiveareas of the catalysts 170, 172 can be preserved.

[0064] In addition, in the illustrated arrangement, the catalysts 170,172 are spaced apart from each other with the distance D1. The catalysts170, 172 thus do not contact each other even if the catalysts 170, 172thermally expand. The solders 192, 196 are subjected to less stress ascompared to the prior design illustrated in FIG. 1. The durability ofthe catalytic device 154 thus is improved while eliminating the need forthe retainers in many applications; however, it is understood that theretainers can still be used with the catalyst device if desired.

[0065] In the illustrated arrangement of FIGS. 6 and 7, the first end200 of the catalyst 170 faces the second end 202 of the catalyst 172,and the second end 198 of the intermediate member 176 faces the firstend 194 of the intermediate member 178. Alternatively, with reference toFIG. 8, both the first ends 200 of the catalysts 170, 172 can face eachother, and both the second ends 198 of the intermediate members 176, 178can face each other. Also, with reference to FIG. 9, both the secondends 202 of the catalysts 170, 172 can face each other, and both thefirst ends 194 of the intermediate members 176, 178 can face each other.

[0066] Additionally, the intermediate members 176, 178 are notnecessarily in some applications. FIG. 10 illustrates a modifiedcatalytic device 210 that has no intermediate members. In thisarrangement, the catalysts 170, 172 are directly brazed to the tubularmember 174. The modified arrangement can provide a simpler catalyticdevice.

[0067] In any embodiments and variations, the catalytic device canincorporate three or more catalysts. The number of the intermediatemembers can change along with the number of the catalysts. Additionally,while the illustrated embodiments disclose each of the intermediatemembers 176, 178 being of the same size (both in length and in diameter)and the catalyst 170, 172 being of the same size (both in length and indiameter), the sizes and shapes of these components can vary and can bedifferent from each other. It is preferred, however, that each catalystof the plurality have generally the same size and shape in order tominimize the cantilevered weight and to minimize the restriction to flowthrough the exhaust passage. For similar reasons, it is also preferredthat each intermediate member of the plurality have generally the samesize and shape.

[0068] Of course, the foregoing description is that of preferredconstructions having certain features, aspects and advantages inaccordance with the present invention. Various changes and modificationsmay be made to the above-described arrangements without departing fromthe spirit and scope of the invention, as defined by the appendedclaims.

What is claimed is:
 1. A watercraft comprising an internal combustionengine, and an exhaust system arranged to route exhaust gases from theengine to an external location, the exhaust system comprising an exhaustconduit and a catalytic device affixed to the exhaust conduit, thecatalytic device comprising a support member extending in the exhaustconduit and a plurality of catalysts supported by the support member,the catalysts being disposed one after another along a flow direction ofthe exhaust gases.
 2. The watercraft as set forth in claim 1, whereineach one of the catalysts has first and second ends and is affixed tothe support member generally at the first end.
 3. The watercraft as setforth in claim 2, wherein the first end of the catalyst is positionednext to the second end of another catalyst.
 4. The watercraft as setforth in claim 3, wherein the first end of the catalyst is spaced apartfrom the second end of the another catalyst.
 5. The watercraft as setforth in claim 2, wherein the first end of the catalyst is positionednext to the first end of another catalyst.
 6. The watercraft as setforth in claim 2, wherein the first end of the catalyst is brazed to thesupport member.
 7. The watercraft as set forth in claim 1, wherein thecatalysts are spaced apart from one another.
 8. The watercraft as setforth in claim 1, wherein each one of the catalysts is affixed to thesupport member via an intermediate member that extends at least withinthe support member.
 9. The watercraft as set forth in claim 8, whereineach one of the intermediate members has first and second ends, each oneof the intermediate members supports the catalyst generally at the firstend and is affixed to the support member generally at the second end.10. A watercraft comprising an internal combustion engine, and anexhaust system arranged to route exhaust gases from the engine to anexternal location, the exhaust system comprising an exhaust conduit anda catalytic device affixed to the exhaust conduit, the catalytic devicecomprising a first support member extending in the exhaust conduit, aplurality of second support members extending at least partially withinthe first support member and being arranged one after another along aflow direction of the exhaust gases, the first support member supportingeach of the second support members, and a plurality of catalysts eachsupported by one of the second support members.
 11. The watercraft asset forth in claim 10, wherein the catalysts are spaced apart from eachother.
 12. The watercraft as set forth in claim 10, wherein each of thesecond support members has first and second ends and supports thecatalyst generally at the second end.
 13. The watercraft as set forth inclaim 12, wherein each of the second support members is affixed to thefirst support member generally at the first end.
 14. The watercraft asset forth in claim 12, wherein the second end of the second supportmember is positioned next to the first end of another second supportmember.
 15. The watercraft as set forth in claim 12, wherein the secondend of the second support member is positioned next to the second end ofanother second support member.
 16. A catalytic device for an internalcombustion engine comprising a tubular member adapted to be disposedwithin an exhaust conduit of the engine, a plurality of catalystsextending in series with one another and disposed at least partiallywithin the tubular member, the catalysts being spaced apart from eachother.
 17. The catalytic device as set forth in claim 16, wherein eachone of the catalysts has first and second ends and is affixed to thetubular member generally at the first end.
 18. The catalytic device asset forth in claim 17, wherein the first end of the catalyst ispositioned next to the second end of another catalyst.